As the penetration of wind energy increases in the electrical grids there may be a need or desire that wind turbines should contribute to the stability of the electrical grids. In some electric grids there may even be requirements in the form of grid codes on how wind turbines should contribute to stabilising the grid.
In a wind turbine the kinetic energy stored in the rotating system may be used for grid stabilization. This is sometimes referred to as the wind turbine may provide inertial response. The stored kinetic energy may be used to boost the generated power from the normal production for a short period of time, i.e. power delivered to the electrical grid is increased while the stored kinetic energy decreases, resulting in a slowdown of the rotor.
A boost can be provided in different ways, but it typically comprises a boost period where the generated power is increased as compared to the pre-boost period (or normal production period) followed by a recovery period, where the kinetic energy in the rotor is build up again to the pre-boost level. The size of the boost, duration of the boost, as well as constraints of the recovery period may be formalized in grid codes or other requirements. An example of a boost requirements, may be that the wind turbine has to be able to deliver a power boost of 5-10% of rated power for a given time period, e.g. up to 10 seconds, and that the turbine must have returned to normal operation after 2 minutes without going below 20% of the pre-boost power level.
It is against this background that the invention has been devised.